Method for obtaining krypton and xenon



May 28, 1957 H. BONNAUD 2,793,511

METHOD FOR OBTAINING KRYPTON AND xenon Fild April 27, 1954 IlllllllllllIlllllllllll United States Patent METHOD FOR OBTAINING KRYPTON AND XENONHenri Bonnaud, Viroflay, France, assignor to LAir Inqmde, SocieteAnonyme pour lEtude et IExploitatron des Procedes Georges Claude, Paris,France Application April 27, 1954, Serial No. 425,959 Claims priority,application France April 29, 1953 8 Claims. (Cl. 62-175.5)

This invention relates to a method for obtaining krypton and xenon froma gaseous mixture such as air, by washing said gaseous mixture with awashing liquid comprising one or more liquefied gases which are morevolatile than krypton and xenon and concentrating the liquid resultingfrom the washing.

In fact, it has been already proposed particularly in the U. S. PatentNo. 2,095,809 of October 12, 1937, for a Process for Obtaining Kryptonand Xenon From Air, to wash a gaseous mixture such as air with acomparatively small amount of a mixture of oxygen and nitrogen forinstance by means of an amount of washing liquid smaller than one tenthof the amount of air in process. The washing in liquid takes almost allthe krypton and xenon contained in the air in process, then the liquidresulting from the washing is rectified and finally a small amount ofliquid or gases containing a high proportion of oxygen is collected,said amount containing practically all the krypton and xenon containedin the air submitted to the washing action.

Owing to the extremely small proportions of krypton and xenon in theatmosphere (respectively l/ 1,000,000 and 1/ 11,000,000) it is verydifiicult to obtain a nearly complete extraction. Nevertheless theparticular uses which are made commercially of said gases and which arelimited only by the quantities available are such that these gases arevery valuable.

The main object of the invention is to provide a method which increasesvery substantially the yield of both of these extracted gases, by usingthe liquid resulting from the washing in the washing step itself.

Another object of the invention is to provide a method wherein theliquid resulting from the washing is used in the washing step afterhaving been submitted to various operations.

In the accompanying drawing forming a part of this specification, thefigure shows diagrammatically and as an example one embodiment relativeto an apparatus for obtaining from atmospheric air a liquid in whichkrypton is comparatively concentrated. This gas will be extracted in thepure state in a further step, not shown. The apparatus thus shown hasall the main features of the invention.

For the sake of clarity, in the present specification and claims,krypton will designate the whole of krypton and xenon contained in air.

The air from which krypton must be extracated, pre viously submitted toa pressure a little above the atmospheric pressure, for instance 1.7absolute atmosphere, and brought to room temperature arrives through apipe 1 and is refrigerated down near its condensation point in a groupof two regenerators 2A and,2 B which run alternately. The heat of theair is thus exchanged accord ing to a known process and passed to thegases purified from krypton. The air which is cooled in the regeneratorscauses the vapor of water and carbonic anydride, both contained in theair, to be deposited. The corresponding deposits are then wept out bythe gases freed of krypton and passing the reverse direction.

The air which is then cooled passes through an expansion turbine 45 andarrives through a pipe 3 at the bottom of a counter-current column 4 inwhich it is washed by liquids the origin of which will be explainedfurther.

This washing column is preferably of a conventional type with superposedhorizontal plates and ascending gas bubbling on each plate in thewashing liquid descending from the top of the column. It could also beof the type with contact elements, such as Raschig rings or similarmembers.

The total amount of the washing liquids is comparatively small withrespect to the amount of the air treated and is for instance about 10%of the latter. The air freed from krypton leaves the column 4 at the topthrough a pipe 5 while the liquid loaded with krypton flows out at thebottom of the column 4, passes through a filter 6 and gathers in thecontainer 7 from which it is extracted by a pump 8. According to theinvention, a part of the liquid returns to the column 4 through a pipe 9provided with a valve 10 while another part is by-passed through a pipe39 provided with an adjusting valve 40 and is injected through a nozzleinto the tube 3 through which the air to be treated arrives to thewashing column 4. The object of injecting this liquid in the gaseous airto be treated is twofold. First, the air to be treated is cooled andbrought down to its dew point before entering the washing column;second, the particles of carbonic anhydride in suspension, which the airto be treated would still contain, and which could choke the firstplates of the column 4, are made heavier and are cooled. These particlesare carried away by the washing liquid and removed by the filter 6.

The liquid which remains arrives through a pipe 11 at the higher part ofa rectifying column 13 and fills up a container 15 from which itoverflows through a pipe 17 in order to descend towards the bottom ofthe column while being more concentrated in krypton. The liquid thusconcentrated is gathered at the base of the column 13 and is extractedby a tube 18 for going to a further step of concentration andpurification.

A gaseous fraction constituted mainly of oxygen, but still containingsmall quantities of krypton, is extracted from the column 13 through apipe 19 the inlet of which is located a few plates above the base. It issent to a tube nest 16 sunk in container 15 arranged at the upper partof the column 13. As this gaseous fraction is mainly constituted ofoxygen it may be liquefied. in the tubular nest 16 owing to the indirectcontact with the liquid of container 15 which contains a high proportionof nitrogen. The liquid that is thus formed in the tube nest 16 is usedaccording to the invention as a washing liquid in the column 4. As itcontains a small quantity of krypton it is sent to this column through atube 20 delivering a few plates below the top. From the top of thecolumn 13 a gaseous fraction containing a small quantity of krypton getsout through a pipe 21. This fraction is first used in an exchanger 22 tocool a liquid the origin of which will be explained further, then itenters through a pipe 23 the base of the washing column.

The washing liquid freed of krypton which is discharged into the top ofthe washing column 4 is obtained in the following way:

An amount of air offor instance 7% of the quantity of air to bewashed iscompressed up to about 20 atmospheres in a compressor, not shown, andarrives through a pipe 123 to an exchanger 24 in which it is cooled bymeans of the portion of the washed air leaving the washing column bypipe 34. It is then expanded down to 4 atmospheres with production ofexternal work in an expansion machine 25 and enters the base of therectifying column 14 which works at the same pressure. The air whichisthen introduced into the column 14 is rectified and gives on the onehand a fraction composed of comparatively pure nitrogen and at any ratefreed from krypton and on the other hand a fraction containing about 40%of oxygen and all the krypton of the air treated in the column 14. Thelatter is connected at its upper part through a condenser vaporizer 26with the rectifying column 13. According to a known device the condensedvapors which ascend in the column 14 produce the calories necessary forheating the base of the column 13. A part of the liquid resulting fromthe condensation of these vapors falls in the column 14. The remainderof the liquid is gathered in the annular gutter 27, leaves the column 14through the pipe 28, is further cooled in the exchanger 22 by thegaseous fraction leaving the top of the column 13, then is expanded bythe valve 29 down to the pressure of the column 4, is finally dischargedat the top of this column and constitutes a part of the washing liquidfreed from krypton. The gas eous fraction leaves the top of the column14 through the pipe 30, goes to an exchanger 31 where it is cooled bythe washed air leaving the top of the column by the pipes and 32. Thisfraction which is at a pressure of about 4 atmospheres is liquefied inthe pipes of the exchanger 31. It is then expanded by means of the valve33 down to the pressure of the column 4 and constitutes the other partof the washing liquid freed from krypton.

The fraction having 40% of oxygen and containing all the krypton of theair treated in the column 14 leaves the latter in the liquid state bythe pipe 38 provided with an expansion valve 41. It is used as anauxiliary washing liquid in the column 4 which it enters at anintermediary height.

The air freed from krypton leaves the top of the column 4 by the pipe 5and is divided into two unequal parts. The smaller goes through the pipe34 and cools, in the exchanger 24, the air providing the washing liquidsof the column 4 and then leaves the exchanger through the pipe 35. Theother part of the air washed goes to the exchanger 31 where it cools andcondenses one of the washing liquids of the column 4, then goes throughthe pipe 36 and cools the regenerator 2A and 2B, and finally leaves thelatter by the pipe 37.

The liquid loaded with krypton and passing through the pipe 18 isdirected to a further step of concentration and purification by knownmeans.

It is to be noted that the different liquids used in the column 3 areintroduced at levels corresponding to their respective concentrations inkrypton. Only the liquids freed from krypton are discharged at the topof the washing column.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred example of the same, and thatvarious changes, particularly in arrangement of parts, may be resortedto without departing from the spirit of the invention, or the scope ofthe subjoined claims.

I claim:

1. A method of obtaining krypton and xenon from a gaseous mixturecomprising washing a gaseous mixture with at least one liquefied gasmore volatile than krypton and xenon, withdrawing the liquid resultingfrom said washing, forcing a part of the liquid resulting from thewashing to the gaseous mixture prior to its washing, and expanding saidpart into said gaseous mixture before washing.

2. The method of claim 1 which comprises concentrating another part ofthe liquid resulting from the washing,

extracting from said part during concentration a gaseous fractioncontaining a small amount of krypton, condensing said gaseous fraction,and introducing said condensed fraction as a washing liquid into theupper portion of the washing column at a stage of the washing operationcorresponding approximately to the concentration in krypton and xenon ofsaid condensed fraction.

3. A method of obtaining krypton and xenon from a gaseous mixturecomprising washing a gaseous mixture in a column with a washing liquidconstituted of at least one liquefied gas more volatile than krypton andxenon, withdrawing the liquid resulting from said washing, forcing apart of said liquid resulting from the washing back to the washingcolumn and using it as a second washing liquid, said part beingintroduced into said column at a height where the concentration inkrypton and xenon corresponds approximately to the concentration of saidliquid in said column.

4, The method of claim 3 which comprises concentrating another part ofthe liquid resulting from the washing, extracting from said part duringconcentration a gaseous fraction containing a small amount of krypton,condensing said gaseous fraction, and introducing said condensedfraction as a washing liquid into the upper portion of the washingcolumn at a stage of the washing operation corresponding approximatelyto the concentration in krypton and xenon of said condensed fraction.

5. A method of obtaining krypton and xenon from a gaseous mixturecomprising washing a gaseous mixture in a column with at least oneliquefied gas more volatile than krypton and xenon, withdrawing theliquid resulting from said washing, forcing the liquid resulting fromsaid washing into at least two paths, expending the liquid in one ofsaid paths into said gaseous mixture before washing, and introducing theliquid in another of said paths into said column at a height where theconcentration in krypton and xenon corresponds approximately to theconcentration of said liquid in said column.

6. A method as in claim 3 wherein the gaseous mixture is air.

7. A method of obtaining krypton and xenon from air, comprising washingair with a liquefied gas rich in nitrogen, withdrawing the liquidresulting from said washing, concentrating at least a part of saidliquid, extracting from said part during concentration a gaseousfraction rich in oxygen and containing only a small amount of kryptonand xenon, condensing said gaseous fraction only by heat exchange withthe liquid resulting from the washing, and introducing said condensedfraction into the upper portion of the washing column at a stage of thewashing operation corresponding approximately to the concentration inkrypton and xenon of said condensed fraction.

8. A method of obtaining krypton and xenon comprising washing air with aliquefied gas rich in nitrogen, collecting the liquid resulting fromsaid washing, concentrating at least. a part of said liquid, extractingfrom said part during the concentrating step a gaseous fraction rich inoxygen and containing only a small amount of krypton and xenon,condensing said gaseous fraction substantially at the same pressure asand by heat exchange with the liquid resulting from the washing, andusing said condensed fraction in the washing operation at a stagecorresponding approximately to the concentration in krypton and xenon ofsaid condensed fraction.

References Cited in the tile of this patent UNITED STATES PATENTS

1. A METHOD OF OBTAINING KRYPTON AND XENON FROM A GASEOUS MIXTURECOMPRISING WASHING A GASEOUS MIXTURE WITH AT LEAST ONE LIQUEFIED GASMORE VOLATILE THAN KRYPTON AND XENON, WITHDRAWING THE LIQUID RESULTINGFROM SAID WASHING, FORCING A PART OF THE LIQUID RESULTING FROM THEWASHING TO THE GASEOUS MIXTURE PRIOR TO ITS WASHING, AND EXPANDING SAIDPART INTO SAID GASEOUS MIXTURE BEFORE WASHING.